Showing papers on "Pulsatile flow published in 1985"

Flow effects on prostacyclin production by cultured human endothelial cells.

Abstract: Endothelial cell functions, such as arachidonic acid metabolism, may be modulated by membrane stresses induced by blood flow. The production of prostacyclin by primary human endothelial cell cultures subjected to pulsatile and steady flow shear stress was measured. The onset of flow led to a sudden increase in prostacyclin production, which decreased to a steady rate within several minutes. The steady-state production rate of cells subjected to pulsatile shear stress was more than twice that of cells exposed to steady shear stress and 16 times greater than that of cells in stationary culture.

Hemodynamics of the normal human carotid bifurcation: in vitro and in vivo studies.

Abstract: The spatial and temporal characteristics of blood flow in the normal adult human carotid bifurcation are investigated by two different methods: in vitro pulsatile flow model experiments using laser Doppler anemometry and in vivo studies employing pulsed Doppler velocity measurements obtained with an ultrasound duplex scanner. Glass and Plexiglas models based upon arteriographic measurements were evaluated with laser Doppler anemometer methods for pulsatile flow. A similarity approach permits the model study to be geometrically and hydrodynamically accurate with respect to the human carotid bifurcation. These parallel but separate approaches were originally performed by the principal authors without knowledge of each others' work. Normal flow patterns in the proximal internal carotid artery are demonstrated to include: unidirectional, helical, transient reversal, and low velocity regions of flows. The characterization of these complex temporal and spatially variant flow fields required the high sample volume resolution afforded by the model study. Pulsed Doppler ultrasound and a novel method of positioning the sample volume permitted a qualitative description of the complex flow velocity fields in the normal human bifurcation. Results of the two methods are compared and a striking similarity between the two methods is observed for the primary and secondary flow features. The problem of associating blood flow velocity disturbances with the presence of intralumenal disease is addressed in the discussion. It is suggested that the flow disturbances associated with the normal carotid bifurcation are different from those associated with intraluminal disease and further, that the secondary flow structures can be usefully employed to establish normalcy.

Evaluation of two prototype devices producing noninvasive, pulsatile, calibrated blood pressure measurement from a finger.

Abstract: We evaluated two prototype instruments that measure pulsatile blood pressure continuously and noninvasively and compared the mean arterial pressure obtained from these devices with that obtained mvasivcly m 17 male surgical patients. Each prototype consisted of an infrared photoplethysmograph mounted inside a finger cuff. The cuff was connected to a pressure control valve, which rapidly changed the cuff pressure so as to maintain a null pressure difference across the finger arterial wall. The resultant cuff pressure rapidly tracked the pulsatile intraarterial pressure. The prototypes reproduced absolute pressure, as well as pressure changes, accurately and linearly over a wide range of mean arterial pressures (from 2 to 164 mm Hg), with an average offset error of 0.8 mm Hg (SD ± 3.8; range, -4.6 to 7.9), a mean scatter error of 5.3 mm Hg (range, 3.6 to 8.6), a mean regression slope of 0.97 (range, 0.79 to 1.22) and a mean correlation coefficient of the regression of 0.96 (range, 0.89 to 0.98). Both prototypes worked satisfactorily on all 17 patients, but not all the time on all patients. In 7 patients, probable arterial spasm prevented measurement of finger blood pressure 12.1% of the time, or 5.4% of the time for all patients. Ninety-six percent of the lost samples occurred with prototype 2, suggesting an instrument-related cause, rather than one related to the principle itself. The prototypes were simple to use and were almost free from artifact. Continuous monitoring for up to 7 hours on a single finger caused no harm to the finger.

Characteristics of vascular hydraulic load in patients with heart failure.

Abstract: Aortic input impedance and hydraulic power were derived from simultaneous catheter recordings of ascending aortic pressure and velocity in eight normal subjects and 11 age-matched subjects with clinical heart failure secondary to idiopathic congestive cardiomyopathy. Resting data revealed the characteristic depression of cardiac output and elevation of systemic vascular resistance in patients with heart failure. The pulsatile component of vascular hydraulic load, characteristic impedance (Zc), was similar in both groups (Zc normal: 85 +/- 30 dyne-sec-cm-5; Zc cardiomyopathy: 93 +/- 33 dyne-sec-cm-5). The oscillatory fraction of aortic input power in patients with heart failure (14 +/- 4%) was also similar to that of normal subjects (11 +/- 2%). The transition from rest to exercise in patients with heart failure was marked by a decrease in the steady component of arterial hydraulic load, although characteristic impedance did not change. A similar qualitative response occurred in normal subjects, although the systemic vascular resistance during exercise remained above normal in patients with heart failure. The modulus of the first harmonic of impedance significantly decreased during exercise in normal subjects but did not change significantly in patients with heart failure. Furthermore, the modulus of the first harmonic of the reflection coefficient decreased significantly during exercise in normal subjects but did not change in patients with heart failure in spite of systemic vasodilation. Exercise appears to impose no additional increase in vascular hydraulic load on the ejecting left ventricle. The similar aortic characteristic impedances in patients with heart failure and in normal subjects, at rest and during exercise, are consistent with a constant oscillatory fraction of input power.

Numerical simulation of fully developed sinusoidal and pulsatile (physiological) flow in curved tubes

Abstract: Numerical solutions of the Navier–Stokes equations for fully developed, sinusoidal and pulsatile flows in curved tubes are presented for conditions not accessible to analytical perturbation methods. Simulations of physiological pulsatile flows in the aortic arch reveal a wide variety of interesting flow phenomena, including: (1) complex secondary flows with up to seven vortices in the half-tube; (2) cascaded vortex structures with vortices embedded within vortices; (3) strong secondary flows with associated wall shear stress nearly as large as the axial component; (4) reversal of axial-flow direction at the inside wall; (5) peak axial wall shear stress at the inside wall; (6) highest r.m.s. wall shear stress at the inside wall; and (7) oscillatory impedance, which is accurately described by straight-tube theory.

Pulsatile Release of Growth Hormone and Prolactin from the Primate Pituitary in Vitro

Abstract: Perifused anterior hemipituitaries from one male and 4 female monkeys released GH and PRL in a pulsatile pattern, with mean ± se interpulse intervals of 8.2 ± 0.4 and 8.5 ± 0.3 min, as determined by a cycle detection computer algorithm. Mean hormone concentrations in the perifusate fractions collected at 2-min intervals were 435 ± 89 (GH) and 515 ± 262 (PRL) ng/ml. Pulse amplitudes averaged 74 ± 16 ng/ml for GH and 189 ± 89 ng/ml for PRL. These findings suggest the presence of a high frequency pulsatile secretory mechanism within the primate pituitary. (Endocrinology 116: 1–5, 1985)

Cardiac gated MR imaging of cerebrospinal fluid flow.

Abstract: This is a preliminary investigation of the cerebrospinal fluid (CSF) spaces using cardiac gated magnetic resonance imaging. A variation of intensity of the signal from the cerebral aqueduct is demonstrated during the cardiac cycle. The pattern of this variation suggests pulsatile CSF flow. Calculations that have been verified by phantom measurements show that CSF flow rates less than 1 mm/s may be detectable. Magnetic resonance may therefore offer a new method for the demonstration and measurement of CSF flow.

A Circle of Willis Simulation Using Distensible Vessels and Pulsatile Flow

Abstract: The development of a one-dimensional numerical (finite-difference) model of the arterial network surrounding the circle of Willis is described based on the full Navier-Stokes and conservation of mass equations generalized for distensible vessels. The present model assumes an elastic wall defined by a logarithmic pressure-area relation obtained from the literature. The viscous term in the momentum equation is evaluated using the slope of a Karman-Pohlhausen velocity profile at the vessel boundary. The afferent vessels (two carotids and two vertebrals) are forced with a canine physiologic pressure signature corresponding to an aortic site. The network associated with each main efferent artery of the circle is represented by a single vessel containing an appropriate amount of resistance so that the mean flow through the system is distributed in accordance with the weight of brain irrigated by each vessel as determined from a steady flow model of the same network. This resistance is placed a quarter wave-length downstream from the heart to insure proper reflection from the terminations, where the quarter wavelength is determined using the frequency corresponding to the first minimum on an input impedance-frequency diagram obtained at the heart. Computer results are given as time histories of pressure and flow at any model nodal point starting from initial conditions of null flow and constant pressure throughout the model. Variations in these pressure and flow distributions caused by the introduction of pathologic situations into the model illustrate the efficacy of the simulation and of the circle in equalizing and redistributing flows in abnormal situations.

Basic concepts for the understanding of large arteries in hypertension.

Abstract: The conventional approach to hypertension considers only the peak and trough of the pressure wave in the brachial artery (systolic and diastolic pressure). An alternate (or supplementary) approach considers mean pressure and fluctuation around this mean. Such an approach permits separation of pulsatile phenomena from steady flow phenomena; it is the basis for description of hydraulic load as vascular impedance and for application of engineering principles to the study of fatigue and degeneration of arteries; it readily explains disturbed arterial function in hypertension in terms of increased peripheral resistance and of increased arterial stiffness. The major effects of hypertension on pressure wave contour, on arterial degeneration, and on left ventricular load are consequences of arterial stiffening rather than of increased resistance. Logical therapy for hypertension should include measures to increase arterial distensibility as well as those to decrease peripheral resistance.

Rat gastric mucosal microcirculation in vivo

Abstract: The superficial gastric mucosal microcirculation was observed microscopically by transillumination in the anesthetized rat. The vessels surrounding the gastric crypts were monitored on a television screen through a microscope and the pictures stored on a videotape for off-line analysis of red cell velocity (VRBC) and vessel diameter. From these measurements microvascular volume flows were calculated. VRBC reached steady values after 1-4 h (mean 2 h) and showed a regular pulsatile flow (4-7 cycles/min) in most experiments. Acid output was measured at regular intervals; 50% of the rats showed no spontaneous acid output, but the others secreted up to 100 mu eq/h. The microvessels in the superficial mucosa were classified into three orders according to their branching hierarchy and relative dimensions, and their distribution per unit mass was estimated. VRBC and volume flow were shown to decrease in the successive orders of the microvessels. Calculation of organ blood flow from microvascular flow data and vessel distribution gave values (21 ml.min-1.100 g tissue-1) that agree with earlier reported values. A higher flow velocity was detected in rats with spontaneous acid output than in those without, but there was a poor correlation between the magnitude of the acid output and VRBC. Pentagastrin (96 micrograms.kg-1.h-1) induced a significant increase in both blood flow and acid secretion. Results from this study indicate that this experimental model is potentially useful for studies of the correlation between acid secretion and mucosal blood flow.

Gonadotropin-releasing hormone pulsatile administration restores luteinizing hormone pulsatility and normal testosterone levels in males with hyperprolactinemia.

Abstract: Hyperprolactinemia in men is frequently associated with hypogonadism. Normalization of serum PRL levels is generally associated with an increase in serum testosterone (T) to normal. To determine the mechanism of the inhibitory effect of hyperprolactinemia on the hypothalamic-pituitary-gonadal axis, we studied the effect of intermittent pulsatile GnRH administration on LH pulsatility and T levels in four men with prolactinomas. All patients had high PRL values (100-3000 ng/ml), low LH (mean +/- SEM, 2.2 +/- 0.1 mIU/ml), and low T values (2.3 +/- 0.3 ng/ml), with no other apparent abnormality of pituitary function. GnRH was administered iv using a pump delivering a bolus dose of 10 micrograms every 90 min for 12 days. No LH pulses were detected before treatment. Pulsatile GnRH administration resulted in a significant increase in basal LH levels (6.7 +/- 0.6 mIU/ml; P less than 0.001) and restored LH pulsatility. In addition, T levels increased significantly to normal values in all patients (7.8 +/- 0.4 ng/ml; P less than 0.001) and were normal or supranormal as long as the pump was in use, although PRL levels remained elevated. These data, therefore, suggest that hyperprolactinemia produces hypogonadism primarily by interfering with pulsatile GnRH release.

Differentiation of male hypogonadotropic hypogonadism and constitutional delay of puberty by pulsatile administration of gonadotropin-releasing hormone.

Abstract: It is not possible to differentiate reliably between male idiopathic hypothalamic hypogonadism (HH) and severe constitutional delay of puberty (CD) on the basis of a standard GnRH bolus test (GBT) or other known endocrine or clinical parameters. Therefore, we studied the response of 17 hypogonadal men, 8 with a diagnosis of HH (age, 15.5-41; bone age, 12.5-19 yr; testes, 1-4 ml) and 9 with CD (age, 14.5-20; bone age, 11-15 yr, testes, 2-10 ml) to pulsatile GnRH stimulation. Basal and peak LH and FSH levels after a single dose of GnRH greatly overlapped between the two groups. In each patient, a spontaneous nocturnal plasma profile of LH and FSH, sampled every 20 min, was followed by a pulsatile GnRH stimulation (5 micrograms iv every 90 min) via a portable minipump for 36 h. Before and after this pulsatile GnRH stimulation, a GBT (60 micrograms/m2 iv) was performed and plasma LH, FSH, testosterone, androstenedione, and dehydroepiandrosterone sulfate were measured. Pulse analysis revealed 0-5 spontaneous nocturnal LH peaks in the CD patients but only one in all of the HH patients. During the 36 h of pulsatile GnRH, mean LH and FSH levels were significantly higher (P less than 0.0001) than during the spontaneous nocturnal profile in all patients (except 1 from each group for LH). The GBT after pulsatile stimulation caused significantly higher (P less than 0.001) LH increments in CD than in HH patients, with no overlap between the two groups (range, 4.1-15.6 in CD vs. 0.8-2.4 mIU/ml in HH). Plasma testosterone rose significantly (P less than 0.01) during pulsatile GnRH from 67 to 155 ng/dl (median) in the CD men, but did not change in the HH group (21 to 22.5 ng/dl). Plasma androstenedione and dehydroepiandrosterone sulfate did not rise in either group. We conclude that, in contrast to other parameters investigated so far, the LH increment in the second GBT after 36 h of pulsatile GnRH allows clear-cut differentiation between CD and HH. These results indicate significantly lower pituitary LH reserve in patients with permanent HH after short term priming of the pituitary by pulsatile GnRH administration.

Experimental investigation of branch flow ratio, angle, and Reynolds number effects on the pressure and flow fields in arterial branch models.

Abstract: An experimental investigation was carried out to acquire an understanding of local pressure changes and flow along the main lumen of arterial branch models similar to the femoral artery of man with three different branch angles (30, 60, and 90 deg) and side branch to the main lumen diameter ratio of 0.4. Effects of branch to main lumen flow rate ratios and physiological Reynolds numbers were found to be significant on the local pressure changes, while that of branch angle was also found to be important. The flow visualization study revealed that the flow separated in the main lumen near the branch junction when the pressure rise coefficient along the main lumen was above a critical value (i.e., 0.35 - 0.46), which was observed to be a function of the Reynolds number. The critical value of the branch to main lumen flow rate ratio was found to be about 0.38 - 0.44 also depending on the Reynolds number. Time averaged pressure distributions for pulsatile flow were similar in trend to steady flow values although they differed somewhat in detail in the main lumen in the branch region.

In vitro pulsatile flow velocity and turbulent shear stress measurements in the vicinity of mechanical aortic heart valve prostheses.

Abstract: A two-dimensional laser Doppler anemometer system was used to study the velocity and turbulent shear stress fields created by various types of mechanical aortic heart valve prostheses under physiological pulsatile flow conditions The prosthetic valves studied were the Starr-Edwards caged ball valve, Bjork-Shiley tilting disc valve, Medtronic-Hall tilting disc valve, and St Jude bileaflet valve The results indicate that all four prosthetic valve designs studied create very disturbed flow fields with regions of flow separation and/or stagnation and regions of elevated turbulent shear stress The maximum values of the mean turbulent shear stresses measured during peak systole were 1200 dynes/cm2 for the Starr-Edwards valve, 1600 dynes/cm2 for the Bjork-Shiley valve, 1000 dynes/cm2 for the Medtronic-Hall valve, and 1050 dynes/cm2 for the St Jude valve The corresponding values during the deceleration phase were about 800, 600, 450 and 800 dynes/cm2, respectively These elevated turbulent shear stresses could cause sublethal and/or lethal damage to blood elements, and, together with the regions of flow separation and/or stagnation, could lead to thrombus formation and/or tissue overgrowth on the valve structure, as observed on the clinically recovered prosthetic valves

Ultrasonic assessment of abdominal venous return. I. Effect of cardiac action and respiration on mean velocity pattern, cross-sectional area and flow in the inferior vena cava and portal vein.

Abstract: Duplex scanning, i.e. combined real time ultrasonography and pulsed Doppler velocity measurement, of the inferior vena cava and portal vein was performed in 85 patients subjected to routine left and right heart catheterization. Mean blood velocity and volume blood flow in the inferior vena cava were found to be pulsatile, reflecting both cardiac action and respiration. Different flow patterns could be related to various heart conditions. The cross-sectional area of the inferior vena cava was also pulsatile, the normal variation with respiration being partial collapse during inspiration and maximum distension at end expiration. In the majority of patients, portal vein flow showed variation with respiration only, maximum flow occurring during expiration. The flow patterns found in the two veins were well in accordance with previous invasive findings in animals. It is concluded that duplex scanning is a useful tool in the assessment of abdominal venous return.

Interaction of left ventricular contraction and aortic input impedance in experimental and clinical studies.

Abstract: Implication of aortic input impedance and left ventricular coupling were investigated in three series of studies. In a clinical study, the ascending aortic flow velocity and pressure were simultaneously recorded from a multisensor catheter, and input impedance was calculated from 8 harmonics of aortic pressure and flow. Left ventricular wall stress was calculated from diameters and wall thickness of cineventriculogram and simultaneous recording of left ventricular pressure. In the experimental study, programmable artificial pulsatile pump was used to control pulsatile blood flow in dogs. The pressure-flow relationship in the arterial system had slightly convex curves toward the pressure axis with a critical turning pressure, so the arterial system had low output--high resistance and high output--low resistance characteristics. Therefore, the failed heart should inevitably eject the blood against stiffened vascular beds. Increased work load of the ventricle as expressed by sustained ventricular wall stress was determined mainly by the exaggerated late systolic pressure due to increased input resistance and increased low frequency pulsatile component of the input impedance. These findings are especially important for relieving additional work load of the ischemic heart, which have higher pressure wave reflection.

Cerebral perfusion in dogs during pulsatile and non pulsatile extracorporeal circulation.

Abstract: Eight dogs were cannulated for left heart bypass. Conventional roller pumps were used for bypass with one of the pump console modified to deliver pulsatile bypass. The experiments were performed at normothermia. Each dog was used as its own control. For measurement of cerebral blood flow (CBF) Xe133 was injected into vertebral artery and the gamma activity elimination over the skull was registered. In addition blood samples were withdrawn from the axillary artery and the sagittal sinus for measurement of blood gases. The CBF to the gray matter of the brain was significantly higher during the periods with pulsatile perfusion (P less than 0.01). This was probably due to decreased total cerebral vascular resistance (P less than 0.001). Mean aortic pressure also decreased when the mode of perfusion was changed from non pulsatile to pulsatile (P less than 0.05), indicating a general decrease of the peripheral vascular resistance. A good correlation was noted between the arteriovenous oxygen saturation difference (AV-O2 diff) across the brain and the CBF (R = -0.77, P less than 0.01).

Gonadotrophins and ovarian steroids in cattle. II. Pulsatile changes of concentrations in the jugular vein throughout pregnancy.

Abstract: Short-term secretion patterns (derived from samples collected from jugular vein cannulae every 20 min for 12 h) of LH, FSH, progesterone, oestradiol-17 beta, oestrone and prolactin were studied every 30 days during gestation in heifers. LH pulse frequency and amplitude was greater during the early (months 1-3) and end (months 8-9) than during mid-gestation when pulsatile LH secretion was almost abolished. The frequency of pulsatile FSH release, which was already twice as fast than of LH during early pregnancy, did not change throughout the whole gestation period. Mean, basal and maximal progesterone concentrations were highest during the first 3 months of gestation, were slightly reduced during mid-gestation and decreased further during the last 2 months preceding parturition. Pulses of progesterone occurred concomitantly with the parallel LH/FSH as well as the separate FSH pulses. Average oestradiol-17 beta concentrations during the first months of gestation were slightly higher than during the mid-luteal phase of the cycle and exceeded during mid-gestation concentrations measured at oestrus. Free oestrone could be detected as early as day 60 of pregnancy. Frequency and amplitude of short-term changes of oestrone increased after the 5th month. Discontinuous secretion of oestrone as well as oestradiol-17 beta was only arbitrarily but never consistently correlated with either each other or with pulsatile gonadotrophin release. Apart form an occasional coincidence with pulsatile release of other hormones prolactin concentrations seemed to depend rather on the season of the year and time of the day than on the individual pregnancy stage.(ABSTRACT TRUNCATED AT 250 WORDS)